The overall objective is to determine the intraovarian and extraovarian endocrine relationships that govern ovarian function during pregnacy in the rat. The functional significance of aromatization in the rat corpus luteum will be investigated with particular attention to the role of intraluteal estadiol in the regulation of progesterone synthesis in the corpus luteum. The role of the luteinized theca interna cell in the normal functioning of the corpus luteum will be investigated by autotransplantation of the preovulatory follicle divested of these cells, followed by observation of the steroidiogenic activity of the luteinizing structure.